1. Field of the Invention
The present invention relates to a head that is used for a thermally-assisted magnetic recording which performs data recording by irradiating near-field light to a magnetic recording medium and decreasing an anisotropic magnetic field of the magnetic recording medium, and also to a head gimbal assembly and a magnetic recording device to which the head is used.
2. Description of the Related Art
In the field of magnetic recording using a head and a medium, further performance improvement of thin film magnetic heads and magnetic recording media have been demanded in conjunction with a growth of high recording density of magnetic disk devices. Currently, composite type thin film magnetic heads are widely used for the thin film magnetic heads. The composite type thin film magnetic heads are configured with a configuration in which a magnetoresistive (MR) element for reading and an electromagnetic conversion element for writing are laminated.
The magnetic recording medium is a discontinuous medium in which magnetic nanoparticles gather and each of the magnetic nanoparticles has a single magnetic domain structure. In this magnetic recording medium, a single recording bit is configured with a plurality of magnetic nanoparticles. Therefore, in order to increase recording density, asperities at a border between adjacent recording bits need to be reduced by decreasing the size of the magnetic nanoparticles. However, decreasing the magnetic nanoparticles in size leads to a decrease in the volume of the magnetic nanoparticles, resulting in a decrease in thermal stability of magnetization in the magnetic nanoparticles.
As a countermeasure against this problem, increasing magnetic anisotropy energy Ku of magnetic nanoparticles may be considered; however, the increase in Ku causes an increase in an anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity of the thin film magnetic head is substantially determined by saturation magnetic flux density of a soft magnetic material configuring a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined by the upper limit of the writing magnetic field intensity, it becomes impossible to write. Currently, as a method to solve such thermal stability problem, a so-called thermally-assisted magnetic recording method has been proposed in which, while a magnetic recording medium formed of a magnetic material with large Ku is used, the magnetic recording medium is heated immediately before the application of the writing magnetic field so that the anisotropic magnetic field is reduced and the writing is performed.
As this thermally-assisted magnetic recording method, a method that uses a near-field light probe (a so-called plasmon-generator) which is a metal piece that generates near-field light from plasmon excited by laser light is generally known.
As a magnetic recording head provided with such plasmon generator, a magnetic recording head provided with a pole, a waveguide, and a plasmon generator having a propagation edge opposing the waveguide has been already proposed by the inventors of the present application. Specifically, a magnetic recording head is proposed in which from the perspective of the air bearing surface side, heat dissipation layers are respectively jointed to trailing side end parts of a substantially V-shaped portion of the plasmon generator which has the substantially V-shaped part that is formed with a propagation edge positioned on the leading side and in which a part of the pole is contained in a space formed by the V-shaped part (U.S. patent application Ser. No. 13/046,117).
In this thermally-assisted magnetic recording head, light propagating through the waveguide is coupled with a plasmon generator in a surface plasmon mode to excite surface plasmon, and the surface plasmon propagates through the plasmon generator so that the near-field light is generated at the near-field light generating portion positioned at an air bearing surface (ABS) side end part of the propagation edge. Furthermore, a magnetic recording medium is heated by the near-field light generated in the near-field light generating portion of the plasmon generator, a writing magnetic field is applied upon a reduced isotropic magnetic field of the magnetic recording medium, and thereby information is written. In the above-described thermally-assisted magnetic recording head, a method that allows steep magnetization reversal between adjacent magnetic domains of the magnetic recording medium and that satisfies the demand of high recording density and high signal to noise (SN) ratio is shortening the distance between the center of near-field light irradiated to the magnetic recording medium and the center of the magnetic field applied from the pole, that is, in other word, shortening the distance between the near-field light generator and a tip end part (the end part positioned on the most leading side on the air bearing surface side) of the pole.
In order to shorten the distance between the near-field light generator and the tip end part of the pole in the magnetic recording head with the above-described configuration, it is necessary to thin the thickness of a substantially V-shaped part of the plasmon generator. However, with the thinned thickness, the light is absorbed by the pole contacting the substantially V-shaped part, and this may reduce light intensity of the near-field light that emits at the near-field light generator. As a result, a preferred thermally-assisted effect may not be obtained. On the other hand, when the thickness of the substantially V-shaped part of the plasmon generator is thickened to obtain sufficient light intensity of the near-field light, the distance between the near-field light generator and the tip end part of the pole is lengthened, and this may bring difficulties to satisfy the demand of high recording density and high SN ratio.
In such a situation, due to demands of further higher recording density in recent years, there is a current situation that the demand for the thermally-assisted magnetic recording head that allows even steeper magnetization reversal between adjacent magnetic domains of the magnetic recording medium and that satisfies the demand of higher SN ratio and higher recording density has raised.